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GNU LESSER GENERAL PUBLIC LICENSE
Version 2.1, February 1999
Copyright © 1991, 1999 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Everyone is permitted to copy and distribute verbatim copies of this license
document, but changing it is not allowed.
[This is the first released version of the Lesser GPL. It also counts as the
successor of the GNU Library Public License, version 2, hence the version
number 2.1.]
Preamble
The licenses for most software are designed to take away your freedom
to share and change it. By contrast, the GNU General Public Licenses are
intended to guarantee your freedom to share and change free software--to
make sure the software is free for all its users.
This license, the Lesser General Public License, applies to some specially
designated software packages--typically libraries--of the Free Software
Foundation and other authors who decide to use it. You can use it too, but we
suggest you first think carefully about whether this license or the ordinary
General Public License is the better strategy to use in any particular case,
based on the explanations below.
When we speak of free software, we are referring to freedom of use, not price.
Our General Public Licenses are designed to make sure that you have the
freedom to distribute copies of free software (and charge for this service if you
wish); that you receive source code or can get it if you want it; that you can
change the software and use pieces of it in new free programs; and that you
are informed that you can do these things.
To protect your rights, we need to make restrictions that forbid distributors to
deny you these rights or to ask you to surrender these rights. These restrictions
translate to certain responsibilities for you if you distribute copies of the
library or if you modify it.
For example, if you distribute copies of the library, whether gratis or for a fee,
you must give the recipients all the rights that we gave you. You must make
sure that they, too, receive or can get the source code. If you link other code
with the library, you must provide complete object files to the recipients, so
that they can relink them with the library after making changes to the library
and recompiling it. And you must show them these terms so they know their
rights.
We protect your rights with a two-step method: (1) we copyright then library,
and (2) we offer you this license, which gives you legal permission to copy,
distribute and/or modify the library.
To protect each distributor, we want to make it very clear that there is no
warranty for the free library. Also, if the library is modified by someone
else and passed on, the recipients should know that what they have is not the
original version, so that the original author’s reputation will not be affected by
problems that might be introduced by others.
Finally, software patents pose a constant threat to the existence of any free
program. We wish to make sure that a company cannot effectively restrict the
users of a free program by obtaining a restrictive license from a patent holder.
Therefore, we insist that any patent license obtained for a version of the
library must be consistent with the full freedom of use specified in this license.
Most GNU software, including some libraries, is covered by the ordinary
GNU General Public License. This license, the GNU Lesser General Public
License, applies to certain designated libraries, and is quite different from the
ordinary General Public License. We use this license for certain libraries in
order to permit linking those libraries into non-free programs.
When a program is linked with a library, whether statically or using a shared
library, the combination of the two is legally speaking a combined work,
a derivative of the original library. The ordinary General Public License
therefore permits such linking only if the entire combination fits its criteria
of freedom. The Lesser General Public License permits more lax criteria for
linking other code with the library.
We call this license the “Lesser” General Public License because it does Less
to protect the user’s freedom than the ordinary General Public License. It also
provides other free software developers Less of an advantage over competing
non-free programs. These disadvantages are the reason we use the ordinary
General Public License for many libraries. However, the Lesser license
provides advantages in certain special circumstances.
For example, on rare occasions, there may be a special need to encourage the
widest possible use of a certain library, so that it becomes a de-facto standard.
To achieve this, non-free programs must be allowed to use the library. A more
frequent case is that a free library does the same job as widely used non-free
libraries. In this case, there is little to gain by limiting the free library to free
software only, so we use the Lesser General Public License.
In other cases, permission to use a particular library in non-free programs
enables a greater number of people to use a large body of free software. For
example, permission to use the GNU C Library in non-free programs enables
many more people to use the whole GNU operating system, as well as its
variant, the GNU/Linux operating system.
Although the Lesser General Public License is Less protective of the users’
freedom, it does ensure that the user of a program that is linked with the
Library has the freedom and the wherewithal to run that program using a
modified version of the Library.
The precise terms and conditions for copying, distribution and modification
follow. Pay close attention to the difference between a “work based on the
library” and a “work that uses the library”. The former contains code derived
from the library, whereas the latter must be combined with the library in order
to run.